That solution might work for getting rid of Jazz fans but unfortunately Mavs fans are racially diverse.
Whatever the North's motivation was to enter the war, the southern states seceded because they perceived a threat to slavery. All other motivations were either secondary and often related to slavery in some sense.
Slavery was the overwhelming motivating factor for southern secession. Of course individuals fighting in the war had their own reasons for doing so. But, as the letter you quoted implies, the question of slavery posed an existential threat to the Union. It effected every other issue because no other issue could be resolved until that question was answered.
